Deposition mechanisms and functions of novel histone H3 and H2A.Z variants

• Applicant: Professorin Dr. Sandra Brigitte Hake
• Subject Area: General Genetics and Functional Genome Biology
• Term: from 2012 to 2014
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 230086546

Chromatin is the biochemical template of all DNA-related eukaryotic cellular processes and its structural conformation needs to be tightly regulated in order to control gene expression, replication and DNA repair. Important players in these regulatory mechanisms are among others specialized histone variant proteins that are incorporated into chromatin in exchange with their canonical counter parts. In humans, several variants of the core histone families H2A, H2B and H3, but not H4, have been identified and although much information on their biological roles has been gathered in the last decades, many functional features remain obscure and are not understood.Over the last three years we were able to publish the discoveries and characterizations of two novel primate-specific histone variants, H3.Y and H2A.Z.2.2. Both variants are incorporated to different degrees into chromatin, show highest expression levels in human brain and have unique and unusual features. H3.Y expression is found in only a subset of cell types, is influenced by nutritional and proliferative stress signals, and it controls the expression of cell cycle-specific genes. H2A.Z.2.2 on the other hand, is a novel alternative splice form of H2A.Z.2, one member of the evolutionary conserved, essential and functionally enigmatic H2A.Z variant family. H2A.Z.2.2 differs in comparison to H2A.Z.1 and 2 in its unique C-terminal sequence and structure and significantly destabilizes nucleosomes. Following our previous successful studies, we now plan to investigate the function of these novel variants in more detail.The aim is to discover and functionally dissect the molecular mechanisms that lead to the targeted chromatin incorporation or ejection of these histone variants. Knowledge of the precise variant chromatin localization sites in vivo, e.g. promoter, coding, non-coding etc. regions, provides an essential step to understanding the biological significance of the respective variant. In initial unpublished experiments, we could partially determine H2A.Z variant chromatin localization in low-resolution and discover all human histone variant chaperone complexes with quantitative mass spectrometry. We propose that H3 and H2A.Z chromatin targeting is achieved by distinct processes. We hypothesize that H3 variants are directly targeted to and deposited into their correct chromatin sites, whereas incorporation of H2A.Z proteins seems to follow a different, still unknown, mechanism. Besides determining the exact chromatin localization sites, we plan to investigate how H3.Y and H2A.Z variants are brought to these regions by identifying those factors responsible for correct chromatin site targeting. Furthermore, we aim at understanding the biological role of both histone variants with regard to gene regulation and chromatin stability.

• DFG Programme: Research Grants